Targeting of flavodoxin to chloroplasts of mesophyll but not bundle sheath maize cells confers increased drought tolerance

Abiotic stresses, especially drought, represent the main factor limiting agricultural productivity world-wide. Maize, one of the top crops in terms of food, feed and biofuel production, is a C4 summer monocotyledoneous species grown as a single-cross hybrid displaying high heterosis (conducive to improved grain yield), and high sensitivity to drought stress at different growth stages (Sheoran et al., 2022). Photosynthesis is an early target of most environmental hardships including drought, which inhibits CO2 assimilation associated with stomatal closing. Under such conditions, reducing power generated by the photosynthetic electron transport chain (PETC) cannot be used in the regenerative step of the Calvin cycle, leading to the accumulation of NADPH, over-reduction of the PETC and downregulation of ferredoxin levels (Tognetti et al., 2006). The excess of excitation energy and reducing equivalents are delivered to adventitious acceptors, mostly O2, with the generation of partially reduced and/or activated energy-rich reactive oxygen species (ROS) such as the superoxide anion radical, hydrogen peroxide and singlet oxygen, which act both as toxic compounds and signaling intermediates (Foyer et al., 2017; Dvořák et al., 2021). Oxidative stress is thus an almost universal outcome of environmental adversities. [...]